How are they useful?
What are film strips?
Film strips are things that look like a line of tape. On each part of a film strip there are little squares. in each square you put in a picture. The pictures are called slides. The slides have to be in a sequence else it will be rubbish!
How do they work?
Well the little pictures in each square are projected. This means that it will put whatever is on the picture will be shown on a bigger screen. If the pictures are in the right order then when the film strip moves it will give the elousion of movemnet.